Screed is too low. Are there standards for this?

Regarding the door "edges" (top or bottom?) or the covering of the lintels, question marks arise for me... doesn't one contradict the other?

The meaning is probably that the frames have slid down due to the unexpectedly low floor height, and now no longer cover the lintel at the top. However, it shouldn't actually have been planned to be fitted flush like that. And it is usually also noted that measurements should be checked on site.

Yes, that's exactly how it is....due to the low floor height, the covers do not obscure the lintel....the BU was supposedly there for measuring. But then really can't...

I think you have weak arguments, because you surely - possibly also indirectly - approved the height of the screed construction. Can't the vinyl floor be underlaid so that it reaches the tile height?

Besides, tiles were never mentioned in the contract. I removed floor covering work and painting work. I just measured. From the floor (i.e. vinyl) to the top edge of the door threshold, there is almost a 5 cm gap. If I have vinyl with a thickness of 6mm and a standard tile is 8mm thick, that does not explain the difference.

Definitely not. There must be sections showing the individual construction thicknesses. Maybe something went wrong with the height transfer from the top edge of the finished floor? Are there meter marks or a marking for the top edge of the finished floor in the house? There should be, actually ...

Another possibility: doors are too small or the lintels are too high ...

Did they perhaps forget a layer of Styrofoam? Can you check at the stairwell (to the basement) or somewhere else?